1 Answer
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You could try running tcpdump or tshark while running your script with

tcpdump -i eth0 -n -p icmp

Somewhere you should see the tcpdump output stop at either an outbound ping request or an inbound ping reply. This, of course, you can do on both the client and the server and see if both machines request and answer correctly.
Since you're using bonding, you might want to tail -f /var/log/syslog or /var/log/messages and see if the kernel logs something about the bond failing over to the slave NIC.